hi am new today, i’ve recently bought a 14 plate zetec fiesta with 78k on clock, few days ago yellow engine light popped up. took it to garage an they said the code is Catalyst System Efficiency Below Threshold they said they 95% sure it needs a new one, but also said could be O2 sensors, been quoted £792 can any one help me with this is this right, don’t know much about cars thanks. kyle